1. Field of the Invention
This invention relates to automatic transmissions for bicycles and other prime movers. More particularly, this invention relates to a multi-speed transmission employing a cluster sprocket assembly, wherein switching of the chain from one sprocket to an adjacent sprocket is controlled by a derailer assembly. Still more particularly, the invention relates to cluster sprocket assemblies having teeth configurations and placements which facilitate movement of the chain from one sprocket to an adjacent sprocket during derailing.
2. Description of the Background Art
Presently, there exist many types of transmissions that employ a cluster sprocket assembly and a derailer assembly for selectively moving a chain from one sprocket to another adjacent sprocket so as to change the speed of the bicycle. Basically, derailers function to exert a force on the chain in a location proximate to the cluster sprocket assembly so as to force the chain into alignment with the adjacent sprocket. During derailing from one sprocket to another sprocket, the chain is forcibly urged off of the teeth of the one sprocket and onto the teeth of the adjacent sprocket. Upon a full revolution, the chain is thus fully derailed from the one sprocket and is fully engaged around the adjacent sprocket, thereby completing the derailing to the adjacent sprocket.
Cluster sprocket assemblies and derailers have been universally accepted throughout the bicycle industry. However, it has also been widely known that the chain may slip during derailing should the teeth of the adjacent sprocket not fully engage the chain as the chain is forcibly moved off the one sprocket onto the adjacent sprocket. Slippage during shifting is highly undesirable as it causes the bicyclist to lose cadence. Moreover, chain slippage during a power stroke may cause the bicyclist to lose control of the bicycle and may even result in an accident.
Heretofore, there have been many attempts to improve upon the derailing of the chain from one sprocket to an adjacent sprocket. Representative patents describing various improvements are disclosed in the following U.S. patents, the disclosures of which are hereby incorporated by reference herein:
U.S. PAT. NO. TITLE 1,202,227 Change Speed Mechanism 3,661,021 Multiple Free Wheel for a Bicycle 3,709,053 Multi-Speed Transmission Front Gear Mechanism for a Bicycle 4,259,880 Multi-Stage Gear Crank for a Bicycle 4,348,200 Multi-Speed Sprocket Assembly for a Bicycle 5,073,151 Multi-Speed Sprocket Assembly for Bicycle 5,085,621 Multi-Stage Sprocket Assembly for Bicycle 5,087,226 Multi-Stage Sprocket Assembly for Bicycle 5,123,878 Multistage Sprocket Assembly 5,133,695 Bicycle Multiple Chainwheel 5,192,248 Multi-Stage Sprocket Assembly for Bicycle 5,192,249 Multi-Stage Sprocket Assembly for Bicycle 5,503,598 Derailleur Arrangement, in Particular for Bicycles 5,690,570 Multi-Stage Sprocket Assembly for A Bicycle 5,716,297 Derailleur Arrangement for Bicycles 5,738,603 Derailleur 5,876,296 Gear Shifting Sprocket Set for Bicycle Chain Wheel
Many of the prior art patents referenced above disclose various types of gear-tooth configurations and placements to facilitate derailing of the chain from one sprocket to an adjacent sprocket. As can be seen in such patents, tooth configuration has heretofore been optimized to allow the chain to twist axially sideways so as to more easily be derailed from one sprocket to an adjacent sprocket. The positions of the teeth on the sprockets are likewise optimized to facilitate derailing. For example, a "missing" tooth configuration has been known to facilitate derailing as the "missing" tooth space more easily allows the chain to be grasped by the tooth of an adjacent sprocket without slippage. U.S. Pat. No. 4,438,200 listed above further provides a "missing" tooth configuration wherein a reduced dedendum radius or recess is provided at the point of the "missing" tooth. A tooth is positioned in the reduced dedendum radius or recess to facilitate shifting of the gear of the chain from one sprocket to an adjacent sprocket by means of the tooth positioned in such recess.
While the foregoing cluster sprocket assemblies noted above have been recognized in the industry as providing some solutions to the problem of slippage during derailing, there is nevertheless a substantial need in the derailer industry for cluster sprockets having configurations that optimize the derailing of the chain from one sprocket to an adjacent sprocket.
Therefore, it is an object of this invention to provide an improvement which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement which is a significant contribution to the advancement to cluster sprocket assemblies for transmissions that facilitate derailing of a chain from one sprocket to an adjacent sprocket without slippage.
Another object of this invention is to provide a cluster sprocket assembly for bicycles and other prime movers wherein the individual sprockets are non-circular in configuration and aligned with adjacent sprockets such that at least one dedendum radius of one sprocket is substantially equal in length and aligned with at least one dedendum radius of an adjacent sprocket, whereby there exists a point in which the dedendum radii of the adjacent sprockets are substantially equal.
Another object of this invention is to provide a cluster sprocket assembly for a primer mover, comprising a plurality of progressively-sized sprockets axially and concentrically positioned relative to one another, the axial positioning of one the sprockets being retarded relative to the axial positioning of an adjacent larger sprocket, the sprockets comprising a non-circular configuration having at least one long dedendum diameter and at least one short dedendum diameter, the short dedendum diameter (e.g., an eccentric oval), of the sprockets being slightly appreciably shorter in length than the long dedendum radius of respective adjacent sprockets, an apex of at least some teeth of the sprockets including a chamfer face, the apex of at least one of the sprockets further including a slanted apex.
The foregoing has outlined some of the pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.